聚丙烯酰胺修饰Fe_3O_4磁性纳米粒子的制备与表征

PREPARATION AND CHARACTERIZATION OF POLYACRYLAMIDE-MODIFIED Fe_3O_4 MAGNETIC NANOPARTICLES

首先通过化学处理在Fe3O4磁性纳米粒子表面引入Si—H键,然后通过选择性的硅氢加成反应制备了一个端基带溴的磁性引发剂,并利用原子转移自由基聚合(ATRP)技术,在该磁性引发剂表面接枝了聚丙烯酰胺高分子,该聚丙烯酰胺高分子展现出分子量高度可控性和窄的分子量分布.经聚丙烯酰胺修饰后Fe3O4磁性纳米粒子的比饱和磁化强度为58.5 emu.g-1,与未修饰纳米Fe3O4相比下降约20%.

Fe3O4 magnetic nanoparticles have been widely used in biomedical applications such as magneticresonance imaging contrast reagent, tissue repair, immunoassay, hyperthermia, drug delivery and cell separation, etc. due to their specific magnetic properties. All these applications require high magnetization values, nanostructure size with overall narrow particle size distribution and special surface coating of the magnetic particles. The latter not only makes Fe3O4 magnetic nanoparticles non-toxic and biocompatible to organism but also provides more chemical selections for molecular device designs. In this paper, Fe3O4 magnetic nanoparticles with mean diameter of about 25nm were prepared by a precipitation method with ferric chloride as starting material, which was partially reduced to ferrous salts by Na2SO3 before alkalinizing with ammonia. XRD analyses showed that the crystal lattice of the magnetic nanoparticles was face centered cubic （fcc） structure. Afterwards, Si—H bonds were imported to the surface of Fe3O4 magnetic nanoparticles by chemical treatment, and then a magnetic-initiator with bromine end groups was prepared from a selective hydrosylation. The resultant initiator was further used to polymerize acrylamide through atom transfer radical polymerization （ATRP）. The grafted polyacrylamide on the surface of Fe3O4 magnetic nanoparticles exhibited the characteristics of ATRP-controlled molecular weights and narrow polydispersity. The molecular mass of polyacrylamide could be modulated by controlling the molar ratio of monomer acrylamide to magnetic-initiator. When the molar ratio was 90, the number average molecular weight was 6440, the polydispersity was 1.19, the molar grafting ratio of polyacrylamide was about 5 %, and the thickness of the surface polymercoatings was about 10 nm. Because it was difficult to directly characterize the surface polyacrylamide of magnetic nanoparticles, so a linear polyacrylamide in the solution was prepared through ATRP to investigate the polymeric structures. Both ^1H-NMR and FTIR exhibited the characteristics of polyacrylamide. DSC measurements showed that the decomposition temperature （ Td ） glass transition temperature （ Tg ） of the surface polyacrylamide of magnetic nanoparticles was 242℃, and the was 102℃, which apparently decreased as compared to that of linear polyacrylamide （Tg = 165℃）. This was because the star structure weakened the interaction of polyacrylamide molecules and reduced the cohesive energies of materials and then made the polymeric chains move more easily. The specific saturation magnetization of polyacrylamide-modified Fe3O4 magnetic nanoparticles was 58.5 emu·g^-1, whichdeclined 20 % compared to that of the non-modified Fe3O4 nanoparticles. The graft of polyacrylamide on the surface of Fe3O4 magnetic nanoparticles can improve the biocompatibility of magnetic nanoparticles, and also endow the particles with more chemical selectivities for the further surface functionalization of magnetic nanoparticles, so these polyacrylamide-modified Fe3O4 magnetic nanoparticles will provide a platform for potential applications in biomedicines.